1. Technical Field
The present invention relates to an electronic component mounting apparatus for mounting electronic components onto a circuit board and, more particularly, to an electronic component mounting apparatus in which a pickup nozzle (suction nozzle) is moved up and down by using a cylindrical cam.
2. Description of Related Art
As a prior art example of the electronic component mounting apparatus in which a pickup (suction) nozzle unit is moved up and down by using a cylindrical cam, one as described in Unexamined Japanese Patent Publication No. 3-8398, which is provided with a cylindrical cam having a fixed-portion and up/down-movable-portion composite cam groove over the entire circumference, is described with reference to FIGS. 8 to 12. It is noted that some cylindrical cams have only fixed cam grooves. In such a case, in the following description of the prior art, the fixed-portion and up/down-movable-portion composite cam groove is replaced by a fixed cam groove, where the fixed cam groove moves a pickup nozzle unit to a specified working position, so that the pickup nozzle unit is positioned at the specified working position, and thereafter a pickup nozzle of the pickup nozzle unit is moved up and down by a rotating cam and a lever mechanism.
Referring to FIG. 8, on a support base 116 are fixed an index unit 101, a cylindrical cam 105, plate cams 109a, 109b, levers 108a, 108b which are actuated by the plate cams 109a, 109b, and springs 110a, 110b which bias the levers 108a, 108b into press contact with the plate cams 109a, 109b, respectively.
The index unit 101 drives a rotating shaft 102 into intermittent rotational motion. A rotary table 103 is attached to a lower end of the rotating shaft 102. Up/down guides 117 which guide the up and down sliding movement of a plurality of pickup nozzle units 104 are fixed at equal intervals on the periphery of the rotary table 103.
Each of the plurality of pickup nozzle units 104 comprises: a block 111 which is inserted in the up/down guide 117 so as to slide up and down; a pickup nozzle 113 inserted in the block 111 in the up/down direction and biased upward toward the block 111 by a spring 118; and a cam follower 112 placed in a fixed-portion cam groove 106 and up/down-movable-portion cam grooves 107a, 107b which are provided in an up-and-down wavy shape over the entire circumference of the cylindrical cam 105 fixed to the support base 116. The cam follower 112 is a roller as shown in FIG. 12.
Next, detailed structure of the fixed-portion cam groove 106 and the up/down-movable-portion cam grooves 107a, 107b of the cylindrical cam 105 as well as operation of the cam follower 112 are described with reference to FIGS. 8 to 11.
Referring to FIGS. 8 to 11, the cylindrical cam 105 is fixed to outside of the rotating shaft 102 in a coaxial state with the rotating shaft 102 that performs intermittent rotational motion, as shown in FIGS. 8 and 9.
In the cylindrical cam 105, as shown in FIGS. 9 to 11, the fixed-portion cam groove 106 as well as the up/down-movable-portion cam grooves 107a, 107b which intervene partly across the fixed-portion cam groove 106 are provided in an up-and-down wavy state over the entire circumference of the cylindrical cam 105. The up/down-movable-portion cam grooves 107a, 107b are provided at specified positions on the circumference of the cylindrical cam 105, i.e., at the locations of a component pickup station and a component mounting station where the pickup nozzle units 104 work. In FIG. 8, the up/down-movable-portion cam groove 107a is positioned at the location of the component mounting station where an electronic component is mounted onto a circuit board 115, while the up/down-movable-portion cam groove 107b is positioned at the location of the component pickup station where a component is picked up from a component feed unit 114.
Then, as shown in FIG. 8, upper ends of the up/down-movable-portion cam grooves 107a, 107b are connected to the levers 108a, 108b, respectively, and the up/down-movable-portion cam grooves 107a, 107b will be slid up and down by the levers 108a, 108b which are actuated up and down by the rotation of the plate cams 109a, 109b, respectively.
Within the fixed-portion cam groove 106 and the up/down-movable-portion cam grooves 107a, 107b, as shown in FIGS. 8 to 11, is placed the cam follower 112. The cam follower 112 is integrally combined with the block 111 that is inserted in the up/down guide 117 so as to slide up and clown as described above. Therefore, when the rotation of the rotary table 103 causes the block 111 to go into intermittent rotational motion around the cylindrical cam 105, the cam follower 112 moves up and down along the fixed-portion cam groove 106 and the up/down-movable-portion cam grooves 107a, 107b while rotating.
In this case, the plate cams 109a, 109b will rotate in synchronization with the intermittent rotational motion of the rotating shaft 102 and the rotary table 103 driven by the index unit 101. However, the plate cams 109a, 109b have such a shape that the levers 108a, 108b will not be actuated during time durations when the cam follower 112 is within the fixed-portion cam groove 106 of the cylindrical cam 105, and as shown in FIG. 11, the up/down-movable-portion cam grooves 107a, 107b will not be moved down until the cam follower 112 reaches the up/down-movable-portion cam grooves 107a, 107b of the cylindrical cam 105. As the up/down-movable-portion cam grooves 107a, 107b move down, the cam follower 112 moves as shown by a cam follower track 119 indicated by two-dot chain line in FIG. 11. While the rotating shaft 102 and the rotary table 103 are at an intermittent rest, the cam follower 112 reaches a lowermost position 119a as shown by the cam follower track 119, at which lowermost position 119a the pickup nozzle 113 is made to perform an electronic component pickup operation or mounting operation. With this operation completed, as the rotating shaft 102 and the rotary table 103 start rotating, the plate cams 109a, 109b make the up/down-movable-portion cam grooves 107a, 107b move upward again, thereby rising them until the up/down-movable-portion cam grooves 107a, 107b coincide with the fixed-portion cam groove 106 of the cylindrical cam 105.
With the above constitution, the operation time of component mounting operation can be reduced in the following way.
By the drive of the index unit 101, the rotating shaft 102 and the rotary table 103 are caused to go into intermittent rotational motion, and the plurality of pickup nozzle units 104 attached to the periphery of the rotary table 103 are caused to start rotating. While the cam follower 112 is within the fixed-portion cam groove 106 of the cylindrical cam 105, the plate cams 109a, 109b are equal in the diameter of operative portion to each other so that the levers 108a, 108b will not be actuated. However, as shown in FIG. 11, when the cam follower 112 has reached the portions of the cylindrical cam 105 corresponding to the up/down-movable-portion cam grooves 107a, 107b, the plate cams 109a, 109b have operative portions in troughs so that the levers 108a, 108b will be actuated, and the up/down-movable-portion cam grooves 107a, 107b will be lowered. During the rest time of the intermittent rotational motion of the index unit 101, the up/down-movable-portion cam grooves 107a, 107b reach the lowermost position 119a, causing the pickup nozzle 113 to perform the electronic-component pickup or mounting operation. With this operation completed, as the rotating shaft 102 and the rotary table 103 start rotating, the up/down-movable-portion cam grooves 107a, 107b move upward again, rising until the up/down-movable-portion cam grooves 107a, 107b coincide with the fixed-portion cam groove 106.
In comparison with the olc type in which the up/down-movable-portion cam grooves 107a, 107b are not provided and the plate cams 109a, 109b will not start operating, neither will the pickup nozzle of the pickup nozzle unit start lowering, before the pickup nozzle unit reaches the location of the next working station, the above-described prior art example accomplishes a reduction in the cycle time of the pickup nozzle by virtue of the arrangement that the pickup nozzle 113 starts its lowering operation midway of the move from one working position to the next working position, so that the pickup nozzle 113 has substantially completed the lowering operation at the time point when it reaches the next working position, in the aforementioned manner.
However, with the construction of the prior art example of the electronic component mounting apparatus in which the pickup-nozzle unit is moved up and down by using the cylindrical cam, both old and new types described above, as shown in FIG. 12, would be required to make the diameter of the roller of the cam follower 112 smaller than the groove widths of the cam grooves 106, 107a, 107b (FIG. 12 shows the cam groove 106 representatively), such that there would necessarily exist a gap G between the roller of the cam follower 112 and each of the cam groove surfaces of the cam grooves 106, 107a, 107b. Accordingly, each time the cam follower 112 changes in the moving direction between up and down, the roller of the cam follower 112 would collide with the cam groove, for example, cam groove surfaces c, e of the cam groove 106 in FIG. 12. Upon this collision, vibrations caused by the collision would transfer from the cam follower 112 to the pickup nozzle 113, thereby causing a shift in the mounting position of the electronic component picked up by the pickup nozzle 113.
Also, because the contacting cam groove surfaces c, e will be changed over between upward movement and downward movement of the roller of the cam follower 112, rotational directions d, f of the roller, which is a rotating member of the cam follower 112, will be changed over upon each changeover of the cam groove surfaces c, e. A change in the rotational directions d, f of the roller of the cam follower 112 would adversely affect the service life of the cam follower 112 such that, particularly when the apparatus is driven at high speed, its service life would be shortened as an issue.